1. Field of the Invention
The present invention relates generally to an apparatus and method for fitting eyeglasses or spectacles. More specifically, the invention relates to an automated eyeglass frame and lens measurement and fitting system.
2. Description of the Related Art
Current eyeglass manufacturing technology does not provide lenses that precisely correct a patient's wavefront aberrations. However, new manufacturing techniques that make use of epoxies, cured to different indexes of refraction matching the wavefront aberrations of a patient, present new manufacturing challenges. Specifically, alignment of the spectacle with the patient's optical axis is of the utmost importance when making spectacle lenses that correct for aberrations other than spherical, cylindrical, and axis. In order to ensure such precise alignment, the distance of the lenses from the cornea's apex, the pupil distance, and the centering of the optic axes of the spectacle lens with respect to the patient's pupil (or visual axis) needs to be accurately measured.
Historically, eye care practitioners have utilized relatively simple methods to determine the positional location of a patient's eye in relation to the spectacle frame. A practitioner typically measures the distance between the pupils, referred to as pupilary distance, and the height from the center of the pupil to the bottom of the spectacle frame or lens. This second distance is referred to as the SEG height. This information is required by the lab to align the optical axis of the lens with the axis of each eye.
One technique utilized has been to simply use a grease pencil to mark the center of the pupil on the lens of the spectacle by “eye balling”, and then using a ruler to measure the pupilary distance (PD) and SEG height. The accuracy of measuring PD has improved in recent years as pupilometers and digital pupilometers have become available. However, pupilometers do not relate PD measurements back to the position of the spectacle frame, nor do they measure other important parameters such as SEG height, vertex distance or pantoscopic tilt. With the advent of progressive addition lenses and the further development of higher order corrective zones, accurate measurement of all these parameters has become even more crucial.
U.S. Pat. No. 5,617,155, to Ducarouge, et al., teaches of a method of measuring the location of spectacle frames in relation to the subject eye using images. Specifically, the patent describes a technique of obtaining locations of the frame and eye automatically by analyzing the luminance gradient in the region of the pupils and the positions of the horizontal and vertical straight lines tangential to the frame. The technique utilizes only one camera and does not provide metrics from the side such as the vertex distance and tilt of the frames in relation to the line of sight.
U.S. Pat. No. 6,659,609, to Mothes, describes a single camera system placed at a distance of preferably 3 m. The device requires the use of a calibration target, which is clipped onto the spectacle frames to provide a spatial reference for determining the scale of the images. Also, as described in the patent, the subject does not look through the device but instead views him or herself in a mirror.
U.S. Pat. No. 5,592,248, to Norton, et al., describes taking several images at different angles to gain information for generating lenses for spectacles. In this patent, use of a single camera is claimed and moved to specific locations to gain the images necessary for 3D reconstruction. Multiple cameras are discussed in text but no description of how these images would be used in conjunction, or how to spatially orient the cameras to one another, therefore, the use of multiple cameras is not enabled in this patent. In addition, image analysis and fiducial landmarks are not utilized to automatically determine the location of the subject's pupil, but are simply measured with a interactive software ruler on the image.
U.S. application Publication No. 20030123026, to Abitbol, et al., describes a 3D camera system primarily intended for modeling and presenting digitally represented spectacle frames on a digitized representation of the subject. However, generating 3D reconstructions of a patient is time consuming and not necessary for generating the basic measurements required for spectacle lens fitting. In addition, the precision of commercially available 3D cameras is not sufficient for accurate placement of high-order corrective zones, which typically require placement of less than 0.5 mm.